Forced Fermentation Test

[Clementine]

HBTers,
has anyone here done a forced fermentation test. I'm suspecting that my LHBS DME is not fermenting out completely. I have had several brews that have not been attenuating as I think they (high 60%ish) should and it is getting progressively worse. On this brew I over pitched massively using a 3 liter starter, I crash cooled, decanted etc and measured at 150ml of clean solid yeast cake of wlp001, I then took that day of the brew and pitched it into 3liters at 0700hrs and it was at high krausen when I pitched the whole starter at 1500hrs. The OG was 1051 on five gallons and the only thing other than 7pounds of DME was 1lb of crystal 60, 0.5lb dextrin , 0.25lb wheat. Now it is stuck at 1.018, so I thought I would do a forced fermentation test. I grew up a 250ml starter from a slant and pitched in 4oz of the wort that was at 1018, added O2 to the head space shook and put it on the stir plate.... nothing, once the CO2 that was in solution came out it was just dead flat beer. I check the SG of the test and it has not moved still sitting at 1018. According to what I have read this is a forced fermentation test accept I was not sure if people did this from the with fresh wort before they even pitch the yeast just to check that their main brew was going to work or if it was only done to problem brews like what I did. I understand this procedure is normally done to AG batches that don't attenuate as a check of is the wort fermentable or if there was a mash problem.

Clem

 

[emjay]

FFT is done with fresh wort.

1.018 doesn't seem particularly "stuck" though, especially since you added dextrin, which is completely unfermentable. If you wanted a very attenuated beer, why did you add it?

 

[jar1087]

I do FFT's on most of my beers, especially lagers and high gravity ales. Generally this means using fresh wort, but I've also done it with fermenting/fermented beer and that also works fine.

I'm a little confused as to what your procedure was; did you add the 4oz of beer to the 250mL starter? Or did you decant the starter, leaving the yeast behind, and then add the beer?

In any case, what I would suggest is taking enough beer for a hydrometer reading, placing it in a sanitized vessel and then adding 1/2 to 1 tsp of dry baker's yeast to the sample. This ensures that you are drastically overpitching into the FFT sample, which will ensure that you get as much attenuation as is possible with that beer. Let this sit for 48 to 72 hours and then take another reading. If this method also shows an FG of 1.018, then I would say that it's as low as it going to go.

In the future, if you want to brew a beer with that same amount of specialty grains, I might suggest replacing a pound of extract with either corn or table sugar; it will help to dry out the beer by fermenting out completely and shouldn't have any effect on flavor at such a low amount. As a side note, I wouldn't recommend adding wheat as a steeping grain; it really needs to be mashed.

 

[Clementine]

Jar1087, thanks for the tip, to clarify this is a recipe I have done in the past and have had good result it normally ends up around 1012 or 1015, I got this recipe for ever ago and I have used it without really thinking about what is in it, good point about the wheat will take that into consideration in the future.

The dextrin (I should have put dextrin malt) just gives it a bit of head retention and I dont think it would be responsible for 4-5 gravity points but I have not checked.

Anyway I digress from the process I used for a FFT. I brewed up in two steps a 250ml starter from a baby food jar agar "slant" then two a 250ml conical flask on a stir plate. This I cooled and decanted completely 99% of the wort before adding the questionable wort about (1.5 hydrometer samples worth) to the jar and returned it to the stir plate.

I will give the bakers yeast a shot and see what that does.

Clem

 

[emjay]

Hmmm... bakers yeast defeats the purpose of a FFT though, because every yeast strain attenuates differently.

If you want to discover and/or diagnosis problems with your main ferment, you need to use:

a) the *same* wort (unfermented), so that your test is equally fermentable, and

b) the *same* strain of yeast, so that you can determine if your main batch underattenuated (by more than a couple points), overattenuated (AT ALL), or hit the mark. If your beer is underattenuated with an FG more than just a couple points over the FG of the test wort, it's likely stuck. If your beer somehow overattenuated and has an FG even LOWER than your test, you are probably looking at an infected batch, unless you made a BIG mistake somewhere.

It should be obvious that if you're using baker's yeast, the results will be pretty meaningless. Compare the attenuation figures of some actual brewer's yeast strains for example, even among the same species (comparing strains from the same companies to ensure consistent methods):

White Labs strains: WLP002 - English Ale Yeast vs. WLP545 - Belgian Strong Ale Yeast
Attenuation: 63-70% & 78-85%, respectively.
—or—
Wyeast strains: 1332 - Northwest Ale vs. (the infamous) 3711 - French Saison
Attenuation: 67-71% & 77-83%

That's a 15% difference between the White Labs strains, and an (average) 11% difference for the Wyeast strains. Who knows how baking yeast compares? Heck, who knows what kinds of variation you see between different brands, even?

I see his reasoning (that it's a cheap way to overpitch in order to attenuate as much as possible), but, as much as I hate to say this about people who are only trying to help - his logic is faulty in just about every way possible. First of all, there are many good reasons to pitch a high cell count of live (aka viability) and healthy (aka vitality) yeast, but attenuation isn't really one of them. Unless the yeast you are using extremely unhealthy yeast and/or are pitching an absurdly low cell count, the effect of pitching rate on the final gravity is pretty negligible - it will probably take the yeast longer to get stuff done and eat all of the sugars that they can, but they want to eat all those sugars, and as long as the viability and vitality remain good, they will continue to do so until they run out of the sugars that they are able to process (or something else happens). Can't really blame the poster for thinking that though - it's an incredibly popular misconception.

The second problem with his reasoning is that, even if you COULD maximize attenuation by pitching an absurd amount of baker's yeast, you wouldn't want to. In fact, it would defeat the whole purpose of doing a FFT in the first place. You are trying to get an idea of what your SPECIFIC COMBINATION of fermentables and fermenter (yeast; buckets, carboys, conicals, etc are properly termed fermentors) should produce, in terms of final gravity. Not only does using a different strain produce an FG that is meaningless to your specific situation, but intentionally messing with the FFT in order to maximize attenuation is worse than pointless, because the only thing that would result from such efforts would be an FFT with a lower FG than your actual batch of beer. And as pointed out above, this would lead to the conclusion that your beer is underattenuated and possibly stuck, whether or not that is actually the case. You'd essentially be creating conditions for a test that greatly increases the chances of a specific conclusion. Not that any of it matters though, because increasing the pitching rate isn't just going to automatically increase the attenuation.

I apologize for the length of the post, and I'm sure I've even been redundant in many parts, but I want to make the purpose of an FFT as clear as possible, as well as help you ensure that your results can allow you to draw meaningful conclusions. So tell me... what kind of meaningful conclusions can you draw by using baker's yeast in your FFT?

 

[jar1087]

@emjay

I have to disagree with your answer for several reasons.

If you want to discover and/or diagnosis problems with your main ferment, you need to use:

a) the *same* wort (unfermented), so that your test is equally fermentable, and

b) the *same* strain of yeast, so that you can determine if your main batch underattenuated (by more than a couple points), overattenuated (AT ALL), or hit the mark.

First, the purpose of a FFT is not to diagnose problems with the fermentation, but rather to determine the limit of attenuation for that specific wort. Because so many fermentation parameters are different between a FFT and a main fermentation, among them time, temperature, pitching rate, oxygenation, and yeast health, even using the same strain, it would be impossible to diagnose exactly what went wrong, if anything, in the main fermentation; the only real data that a FFT gives you is the FG and thus the limit of attenuation for that wort.

I do agree that using the same wort is important, in fact using different wort would completely defeat the purpose of the test. However, using the same strain of yeast is not necessary. In any given wort, there is a certain amount of fermentable sugars and using a different yeast strain is not going to change that; sure some strains are better at fermenting a few sugars, i.e. lager strains with certain trisaccharides, but these sugars make up only a very small amount of the sugars in the wort (max 1-2%). According to Kai (http://braukaiser.com/wiki/index.php/Fast_Ferment_Test) using baker's yeast gives results that are very close to those from other strains and are generally less than .2 Plato (or 0.8 points) off, which is close to the precision of measurements with a hydrometer. Based on those tests, baker's yeast gives FFT results that are anything but meaningless and it is perfectly reasonable to use it, especially when it is suspected that something went wrong with the other strain.

In the examples of commercial yeast that you gave, the stated ranges for attenuation are the values that one could expect in a typical beer style for that yeast. Using the same wort, the differences in attenuation will be much smaller. In fact, the MiniFerment data that White Labs provides bears this out. Unfortunately, they don't have data for the WLP545 that you specified, but they do have WLP550, which has the same stated attenuation range of 78-85% as WLP545. The MiniFerment data for WLP002 and WLP550 show the ethanol to be 4.575% and 4.84% respectively, which, assuming an OG of 1.050, gives attenuations of 69.8% and 73.9% respectively. This 4.1 percentage point difference is much smaller than the 15 percentage point difference indicated by the attenuation numbers and corresponds to an FG of 1.0151 and 1.0131, again assuming 1.050 OG wort. This proves that using a yeast with high stated attenuation cannot magically cause the wort to ferment past its limit of attenuation, it can merely get closer to that limit. (MiniFerment data: http://www.whitelabs.com/beer/strains_wlp002.html and http://www.whitelabs.com/beer/strains_wlp550.html)

Although I may have implied it in my post, attenuation is not the only reason to overpitch, but also to speed fermentation, which is definitely a goal of a Fast Ferment Test.

The second problem with his reasoning is that, even if you COULD maximize attenuation by pitching an absurd amount of baker's yeast, you wouldn't want to. In fact, it would defeat the whole purpose of doing a FFT in the first place.

Not true. You definitely want to maximize attenuation in an FFT and that is exactly the whole purpose of doing an FFT; you want to discover the limit of attentuation for that particular wort. Then either from available data online or from experience with the strain, one can compare how close the strain should come to the limit of attenuation with the results of the main fermentation (see http://braukaiser.com/wiki/index.php/Understanding_Attenuation).

You are trying to get an idea of what your SPECIFIC COMBINATION of fermentables and fermenter (yeast; buckets, carboys, conicals, etc are properly termed fermentors) should produce, in terms of final gravity.

Furthermore, for the reasons that I outlined above, an FFT by its nature is already extremely poorly disposed to determine what results should be expected by a "SPECIFIC COMBINATION" of fermentation parameters.

Finally, and although this may be repetitive, let me stress that the purpose of doing an FFT is to determine the limit of attenuation, that is, the absolute greatest amount of attenuation possible with any yeast strain. Thus, trying to maximize attenuation of the FFT by all means possible, be that temperature, high pitching rate, aeration, etc., is not "worse than pointless," rather that is exactly what one should do. Just because the FFT finishes lower than the beer does not mean the fermentation is stuck, but it does show the limit of attenuation, which can then be used to compare known values for the difference between the limit of attenuation and actual attenuation for a given yeast strain. As shown by Kai's tests, baker's yeast is well suited for determining the limit of attenuation and therefore gives very meaningful results in an FFT. And it's cheap.

I hope this clears up what I meant and what the purpose of an FFT is. I highly recommend Kai's site (braukaiser.com) as a source of information on the subject.

 

[RiverCityBrewer]

+1 what jar1087 said.

Chris White's Yeast book is also a great reference in addition to Kai's site for yeast tests. When I do a forced ferment test I generally use the yeast I'm pitching with, but I usually have the extra yeast to do that with. I have used bakers yeast in the past with fine results.

 

[Clementine]

I can see both points of view both will give some sort of meaningful data.I will play with both bakers yeast as some more wlp001 I have culturing and report back.

Thanks

Clem

 

[jar1087]

emjay is right that using the same strain can be useful, primarily if it's the first time that you have used that strain and don't know how close to the limit of attenuation the yeast will come. However, I also like to compare fermentability between batches and consistently using bakers yeast help me to more directly compare batches, apples to apples, as it were.

 

[emjay]

I don't know what makes you think I implied anything could make yeast "magically ferment past its limit", but I never did. That wouldn't make any sense. What I'm trying to say is that yeast attenuates to varying degrees approaching (but never exceeding) that limit.

As for all yeast strains attenuating pretty close to the same, that's patently untrue. It was almost certainly unintentional, but the MiniFerment data you used amounts to cherrypicking. You want to use the MiniFerment data? Let's do that then.

You point out that the difference the two yeast strains, English Ale and Belgian Ale had an ABV of 4.575 4.84, respectively. A difference of only 0.265, which is definitely small. So let's forget the Belgian Ale then, and look at something else.

How about another yeast from England... WLP023 Burton Ale yeast, with an ABV of 5.16? The difference is suddenly much bigger, with a difference in attenuation of just over 9%.

But as you said, you can't magically attenuate beyond the wort's particular fermentability limit, so there's nothing at all unreasonable about looking at WLP099 - Super High Gravity Ale. Finishing with an impressive ABV of 5.64%, that's over a full percentage-point difference in terms of ABV. And 16.5% difference in attenuation.

So let's not pretend all yeast strains attenuate relatively similarly. Anybody who's used Wyeast 3711 (French Saison) before should know this implicitly. And speaking of Saison yeast, let's look at one more MiniFerment... for WLP565 (Belgian Saison Yeast). This particular yeast finished with an ABV of 4.39% - a full 1.25% lower than WLP099, resulting in the difference in attenuation being a massive 19.3% lower...

Only one problem with that last part... most people who have used WLP565 know it can attenuate FAR better than that. The problem would also be quite obvious - the standard temperature of these MiniFerments (68°) is far too low for at least this particular strain. And this both demonstrates why the MiniFerments don't really give the final word on each strain's ability to attenuate - only at the listed temperature - as well as the fact that there is quite a bit of variation from strain to strain.

As far as being worse than pointless, I was talking about for the OP's purpose. He's trying to see if he should be fermenting further than that. Due to the differences stated above, he would need to use the same strain to figure this out. The only reason for him to use another strain in this FFT is to see if it can bring his FG lower (and by how much) - and I doubt he'll want to use baker's yeast for that.

The usefulness of finding out the absolute limit of fermentability is limited. What do I do with that information? It's nice to know, but it's not something that can really be applied. Plus, given the difference in attenuative abilities that I've demonstrated above, who's to say that baker's yeast attenuates anywhere near the limit?

A friend of mine is a brewer at a fairly large brewery and they do FFTs every time they change something or run into a problem. Chris White also suggests the same (I highly recommend picking up his book), using the same strain to get an idea of whether your batches are attenuating properly and to help you diagnose problems. Using the FFT in such a way yields FAR more useful information, especially for what the OP is trying to solve.